That’s actually with all of them. It’s not a mistake, it’s just the way the instructions are designed.
Every edge of every piece has a black outline in the instructions. The design in the mask is just so complicated that the outline overpowers the green, thus creating a sort of black strip going down the mask.
I believe this is visible on Pohatus instructions as well. It’s not necessarily intentional, but not really a mistake.
I think I noticed the two mask errors in the encyclopedia and those Visorak instruction things. Never thought much about it, though.
But at least I have the encyclopidia in english. The german translation of “Makuta’s guide to the universe” just seems like it was translated by someone who has never heard of Bionicle before and didn’t take the task seriously at that.
A few examples (I’ll try my best to translate them back into english):
many, many errors with singular and plural: In English it would mostly just have been “the” like in “the Toa” could mean “that one Toa” or “these Toa” and the translator(s?) screwed up with this pretty often.
Apparently just one of the Toa Metru was created and the island of Mata Nui faced an invasion by one single Bohrok. Same with Piraka sometimes (seriously, in one sentence it’s the plural and in the next the toa defeated just one Piraka). The Brotherhood of Makuta also just seems to consist out of two beings - Teridax, and his brother, Makuta
(translation) errors: The Toa Hagah stole the mask of light from the Brotherhood, but apparently they brought the mask of time with them to Metru Nui. The Matoran of Le-Koro lived in the treetops between “grapevine shoots” - no wonder then, why they always were so light spirited… The Zyglak were half human. And the Shadow Leech Hive was a beehive.
names - I seriously hope this wasn’t so messed up in the original: Takuta instead of Takua, Vazon instead of Vezon, Mount Valmau instead of Mount Valmai …
Seriously, german kids reading this must have been pretty confused.